@SpacePadreIsle via Twitter
SpaceX is making rapid progress with the construction of their first stainless-steel flight vehicle - Starship SN1, at their South Texas assembly facility. The vehicle's first test flight will take place sometime after March 16, it will fly 20 kilometers above Boca Chica Beach. Last night, SpaceX teams started stacking Starship SN1's stainless-steel barrel and bulkhead section that will makeup the vehicles internal structure.
Elon Musk, the Chief Engineer and founder of SpaceX has been spending the last couple of weeks at the assembly facility in Boca Chica working alongside crews he shared a video clip of Starship's mid section under construction. He had previously explained that the reason they chose to design a stainless-steel flight vehicle is because "it’s obviously cheap, it’s obviously fast -but it’s not obviously the lightest. But it is actually the lightest. If you look at the properties of a high-quality stainless steel, the thing that isn’t obvious is that at cryogenic temperatures, the strength is boosted by 50 percent" Musk explained to Popular Mechanics reporters, "Most steels, as you get to cryogenic temperatures, they become very brittle. You’ve seen the trick with liquid nitrogen on typical carbon steel: You spray liquid nitrogen, you can hit it with a hammer, it shatters like glass. That’s true of most steels, but not of stainless-steel that has a high chrome-nickel content. That actually increases in strength, and ductility is still very high. So you have, like, 12 to 18 percent ductility at, say, minus 330 degrees Fahrenheit. Very ductile, very tough. No fracture issues."
Liquid nitrogen cryogenic strength test underway ☃️ pic.twitter.com/qRPBLInqm0— Elon Musk (@elonmusk) January 29, 2020
In fact, SpaceX recently conducted a cryogenic pressurization test on a propellant dome tank to test the stainless-steel structure also its weld strength under super-chilled temperatures (pictured above). The fuel tank demonstrated that under cryogenic conditions, stainless-steel is strong enough to withstand the pressure it would experience on future human missions to space. The propellant test tank reached an internal pressure of 8.5 bar, the tank needed to withstand a pressure of at least 6 bar for an orbital flight without humans onboard. SpaceX aimed to increase the bar strength to ensure the vehicle ends up being safe for crewed flights. Musk explained other benefits of building a stainless-steel Starship:
"I think is quite important, when you consider this as a reentry vehicle. See, here’s the other benefit of steel: It has a high melting point."
"Much higher than aluminum, and although carbon fiber doesn’t melt, the resin gets destroyed at a certain temperature." He added, "So typically aluminum or carbon fiber, for a steady-state operating temperature, you’re really limited to about 300 degrees Fahrenheit. It’s not that high. You can take little brief excursions above that, maybe 350." Starship is designed to become a fully reusable launch vehicle that must be capable of withstand the highest temperatures upon the fiery atmosphere reentry when returning from space, in order to be reused. When asked where the stainless-steel comes from Musk responded:
"It’s just 301 stainless. Let me put it this way: 304 stainless is what they make pots out of. There’s plenty of it."
This makes Starship production a bit more cost effective compared to the production of other rockets, "The carbon fiber is $135 a kilogram, 35 percent scrap, so you’re starting to approach almost $200 a kilogram. The steel is $3 a kilogram." So, stainless-steel is the most affordable option that offers strength and heat-shield properties. This year the rocket company could build up to 20 test flight prototypes that they will use to preform high-altitude flights that will test the vehicles design and Raptor engines' power. They also aim to conduct Starship's first orbital-flight test before this year ends.
Manufacturing several Starship's this year will sure test out the company's ability of building a Starship production assembly line under a tight schedule. In the future, they have plans of manufacturing at least two Starship vehicles per week in order to achieve transforming humanity into a spacefaring civilization. The final version of Starship will need to be capable of being reused several times per day, as well as take megatons of cargo per year to Mars to establish and maintain a permanent human settlement. So, one day SpaceX will build 100 Starship's per year! For now, Starship SN1 will be the first fully assembled vehicle that will conduct a 20km flight -with production of Starship SN2 flight vehicle simultaneously underway.
About the Author
Evelyn J. Arevalo joined Tesmanian in 2019 to cover news as a Space Journalist and SpaceX Starbase Texas Correspondent. Evelyn is specialized in rocketry and space exploration. The main topics she covers are SpaceX and NASA.